Inspection device for crystal defect of silicon wafer and method for detecting crystal defect of the same

ABSTRACT

The present invention provides an inspection object silicon wafer for the purpose of detecting crystal defects and the method of detection thereof, which make easy the detection of the number and location of the defects formed on the surface of the silicon wafer by performing heat treatment and epitaxial growth under a temperature condition in which the natural oxide film is removed but the state of the surface of the silicon wafer is preserved, specifically under a hydrogen atmosphere of normal pressure and a temperature between 900° C. and 1080° C., through which defects having pits and projections are generated on the surface of the epitaxial layer. and by detecting the defects having pits and protrusions by a light scattering type particle inspection apparatus.

FIELD OF THE INVENTION

[0001] The present invention relates to a silicon wafer for the purposeof detecting crystal defects and the method of detection thereof,specifically to a silicon wafer for the purpose of detecting crystaldefects and the method of detection thereof, in which crystal defectsformed on the surface of the silicon wafer are shown up in pits andprojections by forming epitaxial layer.

TECHNICAL BACKGROUND

[0002] A silicon wafer is the general term for a silicon single crystalsubtrate (hereafter may be referred to as “mirror surface wafer”) madeby slicing the single crystal grown by Czochralski method (CZ method) orFloating zone melting method (FZ method) to thin plate and furtherpolishing the surface to a mirror surface state (hereafter may bereferred to as “mirror surface wafer”) or a silicon epitaxial waferobtained by forming a thin film of silicon single crystal on the mirrorsurface wafer by vapor phase growth. A variety of crystal defects suchas point defect, line defect, plane defect, etc. are formed in a siliconwafer. Among these, the one appearing on the surface (hereafter may bereferred to as “surface defect”) exerts an influence to the electriccharacteristic of semiconductor devices having circuits formed in nearproximity to the surface of the silicon wafer, and the adequate controlof the condition of detect generation is needed.

[0003] As the surface detect has ordinarily no virtual pit orprojection, it is shown up in pit or projection by preferential etchingto be detected. Sirtl solution, Secco solution, and Wright solution arewell known as solutions for preferential etching. For example, Seccosolution is a aqueous solution of 28.86 mol of 50% hydrofluoric acid and0.15 mol of potassium bichromate (K₂Cr₂O₇). These are etching solutionswhich oxidize silicon with the oxidizing agent and solve the oxide filmwith hydrofluoric acid. Crystal defects are made apparent by producingpits and/or projections through a phenomenon that the speed of oxidationby the oxidizing agent differs between oxidation of perfect crystal andthat of a region where crystal defects or stresses exist.

[0004] Surface defects made apparent by the preferential etching areobserved by a normalski type differential interference microscope todetermine its density. The normalski type differential interferencemicroscope gives a three-dimensional appearance of irregularity andruggedness of height of 3.5 nm or higher, and the inclination of planeis observed as a difference in interference color.

[0005] The density of surface defects is determined by observing 5 to 9points of area or scanning in the direction of diameter by 100× to 400×magnification. The number of defects per silicon wafer is worked outfrom the detected number of defects and the measurement area.

[0006] For example, when a silicon wafer of 200 mm diameter is scannedin the direction of diameter in the shape of a cross by the differentialinterference microscope, if the diameter of the field of view of themicroscope is 1.7 mm, then the measurement area is:

1.7 mm×200 mm×2=680 mm².

[0007] Supposing that one surface defect is observed by the scanning,the number of surface defects per silicon wafer is:

1(defect)×(π×100² mm²)÷680 mm²

46(defect).

[0008] The above value 46 of the number of surface defects per siliconwafer is effective only when the surface defects are distributed evenly.When the surface defects appear localized in a region, the above valuediffers far from the real state. Also, when the density of surfacedefects is small, for example, when the number of surface defects persilicon wafer of diameter of 200 mm is under 46, there is highprobability that no surface defect exists in the region scanned by themicroscope and detection is substantially impossible.

[0009] Further, in the case of a silicon wafer of resistivity of 0.02Ωcm or smaller, surface defects are difficult to appear by etching withaforesaid preferential etching solutuon.

[0010] On the other hand, there is visual inspection using collimatedlight as a method of simply inspecting the whole surface of a siliconwafer.

[0011] In the visual inspection, when the surface of apreferentially-etched silicon wafer is irradicated by collimated light,scattered light is reflected from surface defects. The distributionpattern of the surface defects is observed by viewing the scatteredlight in a darkroom. But, by this visual inspection, mapping of thesurface defects on the whole surface can not be obtained by using amachine, and the accurate determination of the number and location ofsurface defects is not possible.

[0012] Also, when trying to detect the surface defects appearing on thesurface of the silicon wafer by preferential etching by means of thelight scattering type particle inspection apparatus, the etched figuresgenerated by the preferential etching are detected similarly asparticles together with the surface defects, and the surface defects cannot be discriminated from the etched figures.

SUMMARY OF THE INVENTION

[0013] The present invention was made to solve the aforementionedproblem. Accordingly, the object of the invention is to provide asilicon wafer on the surface of which the number and location of crystaldefects generated can be easily detected and the method of detectionthereof.

[0014] Usually, before performing epitaxial growth, heat treatment isperformed in a hydrogen atmosphere at normal pressure and a temperaturebetween 1100° C. and 1200° C. for etching the natural oxide film formedon the surface of a silicon wafer and for etching the silicon surfacefor the purpose of eliminating the crystal defects generated on thesurface of the silicon wafer. The etching of the natural oxide film andthat of the silicon surface are instantly completed at theabove-mentioned temperature range. Then, by vapor phase growth ofsilicon single crystal thin film on the surface of the cleaned siliconwafer, an epitaxial layer with largely reduced surface defects isformed.

[0015] The etching of the natural oxide ilm by hydrogen can be effectedat temperatures above 900° C. at normal pressure, but, on the otherhand, the speed of etching a silicon surface by hydrogen decreasesrapidly when the temperature of heat treatment is lower than 1100° C.and the etching hardly occurs below 1080° C.

[0016] Therefore, if a silicon wafer is heat-treated at a temperaturebetween 900° C. and 1080° C. in a hydrogen atmosphere of normalpressure, the natural oxide film is completely removed but the surfaceof the silicon wafer is hardly etched, thus the surface condition ispreserved and also the surface defects are preserved without beingremoved.

[0017] After this heat treatment, if a silicon single crystal film isgrown in vapor phase on the silicon wafer at a temperature between 900°C. and 1080° C. at normal pressure, the surface defects are preservedduring the vapor phase growth and transferred to the epitaxial layer.Thus, the surface defects on the silicon wafer become apparent on thesurface of the epitaxial layer as crystal defects having pits and/orprojections.

[0018] As the crystal defects appearing on the surface of the epitaxiallayer have pits and/or projections, they are detected by a lightscattering type particle inspection apparatus like particles aredetected.

[0019] The present invention was made based on the above mentionedfindings. The inspection object silicon wafer for the purpose ofdetecting crystal defects is characterized in that epitaxial growth ismade on the surface of a mirror surface wafer which the natural oxidefilm is removed of without surface defects being eliminated to make thecrystal defects having pits and/or projections appear on the surface ofthe epitaxial layer.

[0020] The inspection object silicon wafer for the purpose of detectingcrystal defects is manufactured through a process of heat treatment inwhich the natural oxide film is removed without the surface defects of amirror surface wafer being eliminated, and a process of epitaxial growthin which the epitaxial growth is made on the surface of the mirrorsurface wafer and the crystal defects having pits and/or projection aregenerated on the surface of the epitaxial layer.

[0021] More concretely, the heat treatment process and epitaxial growthprocess are preferably performed under a hydrogen atmosphere of normalpressure at a temperature between 900° C. and 1080° C.

[0022] The crystal defect detection method according to the presentinvention relates to a detection method which can easily detect thenumber and location of the crystal defects formed on the surface of asilicon wafer by use of said inspection object. The method ischaracterized in that; by making epitaxial growth on the surface of asilicon wafer heat-treated under a temperature condition in which thenatural oxide film is removed but the surface state of the silicon waferis preserved, crystal defects having pits and projections are made toappear on the surface of the epitaxial layer; and the crystal defectshaving pits and projections are detected by a light scattering particleinspection apparatus. Further preferably the heat treatment and thegrowth of epitaxial layer are performed under a hydrogen atmosphere ofordinary atmosphere at a temperature between 900° C. and 1080° C.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG.1 is a graph showing the correlation between the number ofetch pits and that of particles corresponding to that of crystal defectson epitaxial layer surface.

[0024] FIG.2 is a map showing the distribution of the crystal defectsformed on the surface of a silicon wafer. In the drawings, referencenumber 1 denotes an inspection object for the purpose of determiningcrystal defects, reference number 2 denotes crystal defects.

BEST MODE FOR CARRYING OUT THE INVENTION

[0025] A preferred embodiment of the present invention will now bedetailed with reference to the accompanying drawings. It is intended,however, that unless particularly specified, dimensions, materials,relative positions and so forth of the constituent parts in theembodiments shall be interpreted as illustrative only not as limitativeof the scope of the present invention.

EXAMPLE

[0026] Nine p type silicon single crystal rods of diameter of 200 mm andof resistivity of 0.01 Ωcm˜0.02 Ωcm were prepared, each rod havingdifferent crystal defect density by varying the pulling-condition of thesingle crystal and/or the inside structure of the furnace. Then, thesilicon single crystal rods were sliced to thin plates, and the surfaceof the sliced plates were mirror polished to obtain mirror surfacewafers of plane orientation of (100). The mirror surface wafers obtainedfrom each silicon single crystal rod were separated into two groups, onefor preferential etching and another for vapor phase growth.

[0027] The mirror surface wafers for preferential etching were etched bysaid Secco solution, and the surface defects appearing as etch pits bythe preferential etching were observed by means of a Normalski typedifferential interference microscope.

[0028] The observation by the microscope was done by scanning the mainsurface of the preferentially etched mirror surface wafers by 100×magnification in the direction of diameter in the shape of a cross, andthe number of etch pits per wafer was calculated from the number of etchpits observed and the measurement area.

[0029] On the other hand, the mirror surface wafers for vapor phasegrowth were placed in a vapor phase growth furnace held to a hydrogenatmosphere, and after three minutes of heat treatment at normal pressureand a temperature of 1050° C., trichlorosilane(SiHCl₃) gas was suppliedwhile keeping the temperature of 1050° C. to allow an epitaxial layer of4 μm thick and resistivity of 5 Ωcm to grow at normal pressure. Thustreated wafers were prepared as inspection object silicon wafers.

[0030] When said inspection object silicon wafers for the purpose ofdetecting crystal defects, which are mirror surface wafers withepitaxial layer formed on the surface, were measured by a lightscattering type particle inspection apparatus, crystal defects such asstacking faults(SF) and dislocation defects having pits and/orprojections were apparent on the surface of said inspection objects anddetected as particles.

[0031] In the example, particles equal to or larger than 0.1 μm indiameter were detected over the whole surface of the inspection objectwafers excluding the peripheral part of 5 mm from the outer edge of eachwafer.

[0032] FIG.1 shows a correlation between the number of particles on thesurface of the epitaxial layer and that of etch pits measured by thelight scattering type particle inspection apparatus in the example.

[0033] From FIG.1, it is recognized that there is a good correlationbetween the number of particles and that of etch pits.

[0034] FIG.2 shows an example of measurement of crystal defects 2appearing on the surface of the inspection object wafer 1 manufacturedaccording to the aforementioned procedure.

[0035] From FIG.2, it is recognized that the number and location of thecrystal defects formed on the surface of the mirror surface wafer areeasily determined, for the crystal defects 2 appearing on the surface ofthe epitaxial layer grown under the condition mentioned above can beoutput in a map state all over the surface of the wafer 1 throughdetection by the light scattering type particle inspection apparatuslike conventional particles have been detected.

[0036] Further, although in the example it was shown that the number andlocation of crystal defects formed on the mirror Surface wafer was ableto be detected by a light scattering type particle inspection apparatus,but also the identification of the kind of defect is possible bythinning the crystal defect part by use of a Focused Ion Beam apparatusbased on the detected information on the defects and observing the partby a transmission electron microscope.

[0037] Still further, the present invention is adaptable not only towafers having defects caused by crystal growth but to wafers havingdefects caused by machining in the process of manufacturing mirrorsurface wafers.

[0038] For example, discremination of defects caused by crystal growthfrom those caused by machining is possible in the way in which defectson the surface of an inspection object wafer according to the presentinvention are detected, then the epitaxial layer on the surface of theinspection object wafer is removed by mirror polishing or bynon-selective etching by use of mixed acid of hydrofluoric acid andnitric acid, etc. to get a mirror surface, and after an epitaxial layeris grown again by the method according to the present invention, defectsare detected by a light scattering type particle inspection apparatus.

[0039] Although, in the example, measurement object wafers were mirrorsurface wafers, silicon wafers other than the mirror surface wafers areadaptable, for example, an epitaxial wafer of which the surface is againmirror polished and which having virtually no pits and projections, asfar as pits and projections are generated by epitaxial growth.

INDUSTRIAL APPLICABILITY

[0040] As cited above, by use of the inspection object silicon wafer andmethod of detection of surface defects according to the presentinvention, the number and location of the surface defects formed on thesurface of the silicon wafer can be detected.

1. An inspection object silicon wafer for the purpose of detectingcrystal defects characterized in that epitaxial growth is made on thesurface of a mirror surface wafer which the natural oxide film isremoved of without surface defects being eliminated to make the crystaldefects having pits and projections appear on the surface of theepitaxial layer.
 2. An inspection object silicon wafer for the purposeof detecting crystal defects manufactured through a process of heattreatment in which the natural oxide film is removed without the surfacedefects of a mirror surface wafer being eliminated and a process ofepitaxial growth in which epitaxial growth is made on the surface of themirror surface wafer and the crystal defects are generated as defectshaving pits and projection on the surface of the epitaxial layer.
 3. Aninspection object silicon wafer for the purpose of detecting crystaldefects according to claim 2 characterized in that the heat treatmentprocess and epitaxial deposition process are performed under a hydrogenatmosphere of normal pressure at temperatures conditions of between 900°C. and 1080° C.
 4. A method of detecting crystal defects of a siliconwafer characterized in that; by making epitaxial growth on the surfaceof the silicon wafer heat-treated in a temperature condition in whichthe natural oxide film is removed but the surface state of the siliconwafer is preserved, crystal defects having pits and projections are madeto appear on the surface of the epitaxial layer; and the crystal defectshaving pits and projections are detected by a light scattering particleinspection apparatus.
 5. A method of detecting crystal defects of asilicon wafer according to claim 4 characterized in that, the heattreatment and the growth of epitaxial layer are performed under ahydrogen atmosphere of ordinary atmosphere at a temperature between 900°C. and 1080° C.